I encountered the pair in the same area two days later. Again one of them tore a thin strip of bark from the same white birch, then flew off with it in the same direction as before. This time when I followed them I found the nest. To my surprise it already looked fully formed, hanging, like all vireo nests, in the fork of a twig. It was not in a conifer as I had expected, but instead about four meters from the ground in the aforementioned tall chokecherry bush. This was the first time I had ever seen a blue-headed vireo nest in a deciduous bush or tree.
A second blue-headed vireo nest was not far from this one, and I found it too by following a pair. One or both birds made short purr sounds that seemed like whispers in and around an area of dense conifers. I often lost sight of them, then sometimes saw only one that perched and preened in the trees. Their nest was suspended near the end of a branch in a large balsam fir tree, about six meters above the ground. Sensing a possible story, I wanted to photograph these vireos feeding their young. Since they would not come close to me, I had to get close to them. Over the next several days I built a platform, attached a hide in the form of a little hut to it, and placed it in the tree next to the nest so my 18–55mm lens could reach it.
Throughout my construction of the bird blind, one of the vireo pair was almost always incubating on the nest. It did not flush or seem concerned by my presence. On several occasions it sang next to me; I had expected alarm calls but never once heard them. And yet these vireos were not inattentive. One day a male blackburnian warbler took a bath in a puddle near the nest tree, then flew up to a branch and started to preen. One of the vireos swooped on him and chased him off, making a strikingly scratchy noise all the while.
Later on I fared no better.
When I settled into the blind to start photographing, one or both vireos scolded me in loud raspy and scratchy chittering that reminded me of fingernails scraping across a solid surface. One picture of the pink-yellow naked babies hunkering down was all I got, and was happy to get, before two days of heavy rain (May 29–30) curtailed my efforts. Then came one gorgeous day followed by three more days and nights of torrential rain. The nestlings somehow survived, but the parents remained too wild for me to photograph them, so I switched my attention to the atypical nest in the chokecherry bush.
The bush was too thin to climb, but the nest was low enough to look into from a four-meter stepladder. To let the birds get used to the ladder, I first placed it about ten meters from the nest, then moved it closer each day for several days. The incubating bird sitting on the nest never budged, even when the ladder was right at the nest. When I climbed up to photograph the four eggs, it hopped off briefly, then settled back into place and ignored me. The four eggs were mostly white and were about ready to hatch. (When freshly laid, the eggs are colorless and have thin, pearly transparent shells that later look chalky.)
On May 31, hoping to see young, I again very slowly climbed the ladder to the nest, talking to the incubating bird softly in the hope that it would understand that I didn’t intend to do harm. It now remained still even as I got my camera lens within a half-meter of it.
Four days later, after three all-day and all-night torrential rains, I went back expecting to see either young birds or an abandoned nest. Instead I again found eggs in the nest—but now only three, not four. An egg could not have disappeared on its own from the vireos’ deep nest cup, and a raiding predator would not have daintily plucked out just one egg and otherwise left the nest in pristine condition.
Two days later, on June 6, I checked the nest again. A bird was sitting on it as before. I talked to “her” as before, and she swiveled her head in my direction. Even when I leaned directly over the nest to take pictures she didn’t budge. Deciding to try for a close-up, I pulled the branch with the nest toward me and held it against the ladder. She still showed no sign of alarm. On an impulse I reached over and put my fingers under her belly. When she did not object, I gently lifted her to expose the eggs and with my other hand took a picture of her, the nest and eggs, and my fingers under her. At last she stood up, hopped out of the nest, landed on a twig next to me, and sang! So it seemed the bird was not a female as I had presumed; it was more likely a male, as its song was typically sung by blue-headed vireo males.
A blue-headed vireo on its nest, with the author’s finger reaching under its belly.
I got another surprise when I looked into the nest: it now contained only two eggs. Another egg had disappeared.
I found the nest abandoned a day or so later. The pair’s departure was probably not due to direct soaking by the rain, because vireo nest-lining is coarse, apparently built to allow water to drain through it without collecting in its open-cup structure.
In trying to fathom what had happened I first examined the two remaining eggs. Each contained a decaying embryo. One of them had been dead for at least three days, but the other had died earlier.
The seemingly unending cold, wet weather was the most likely killer. Insects had become scarce. One of the parents might have been killed, as I had not recently seen two birds at this nest.
And two eggs had been removed. I had seen a similar egg reduction before: in a phoebe nest that was being incubated during a freeze in 2011. On March 23 it held one egg. Three frosty days later there was still only one egg when four would have been typical, but on March 29 there were three. I expected incubation to start then, but instead, when I next checked the phoebes’ deep nest cup, the number of eggs had been reduced to two. The parents incubated these two, and two young later fledged from that nest.
Had the vireos voluntarily reduced the number of eggs to match the dwindling food supply? The number of eggs various species lay is affected by the availability of food; fewer eggs are laid when it becomes scarce. When the food supply diminishes during the nestling stage, the number of young fledged is often lower than the number of eggs laid because of starvation or siblicide. If an extra egg, such as a cuckoo’s egg, is added, it may be tossed out. But I had not known of any birds exercising control over the number of their own eggs after laying. In this vireo nest, had all of the eggs hatched and the unexpected bad weather continued, the death of all the young would have been almost certain. But, by halving the brood, the parents might give at least some a chance to live. Birth control is practiced in any case, voluntarily or involuntarily. To date, parental egg reduction has not been proven. It would be incredibly difficult and require astronomical luck to be observing at the moment when a wild bird removes one of its eggs from the nest, and it would be morally indefensible to try to test the hypothesis experimentally. However, brood reduction is certainly more efficient economically than infanticide, which takes place after the wasted effort of incubating and feeding the doomed offspring.
The usual methods of reducing brood size to accommodate food supply are more cruel and less efficient. In eagles and herons one of the young eats the others or shoves them out of the nest. At the same time the vireos were reducing their number of eggs, in other nests I was watching, four tree swallow babies (two of which almost made it to the fledging stage) and five red-breasted nuthatch chicks died of starvation.
8
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Nuthatch Homemaking
IN FEBRUARY OF 2009, I ROUTINELY NOTICED A PAIR OF red-breasted nuthatches near my back door in Vermont. They typically inhabit dense spruce forests. Here there were just a few white pines, but the nuthatches probably stayed because of the constantly available sunflower seeds in my feeder.
On March 14, while there was still much snow on the ground and the beaver pond was still frozen over, the pair was examining dead tree stumps, and for a few minutes I heard a soft and steady tapping on a poplar stump. Unlike woodpeckers, which tap on trees to find grubs and to excavate a home site, red-breasted nuthatches hammer at wood to make a nest cavity, in which they also build a nest. So it was clear that these two were getting interested in making a home, testing various sites. Later that same day they started hammering near the top of a recently dead
red maple tree trunk. The wood was hard, but they stayed, evidently preferring it to the softer poplar they had just tried. Progress was slow. Seven days later they had managed to excavate only an entrance hole. When either of them went in to work on deepening the hole, the end of its tail stuck out.
The red-breasted nuthatch, a tiny bird weighing only about as much as two nickels, tackles a challenging homemaking task. Unlike the local white-breasted and the European nuthatch species, which seek out and use existing shelters, this nuthatch hammers out a nest cavity in solid wood. The European species reuses existing shelters such as old woodpecker cavities and refits the too-large entrance holes by cementing them partially shut with soft mud that dries in place. The white-breasted nuthatch also uses preexisting cavities, but it does not reduce the size of their entrances. The homemaking progression of these three species resembles that of humans possibly first choosing a cave, then reducing the size of the cave entrance with logs and stones, to make the cave into an independent dwelling that can be furnished for comfort on the inside.
Portraits of a red-breasted nuthatch pair.
To excavate an entire nest hole in solid wood, the tiny red-breasted nuthatch has to start early. “Early” is relative to everything else in the flow of the season. By March 27, after almost two weeks of labor, when the snow was melting and the ice on the beaver pond had a ring of water around the edge, only the tip of a tail showed when the bird worked. I recognized the female (by her paler head and chest coloration) as the one doing the heavy work. She hammered in four- or five-second bursts, backed out of the hole tail first with wood chips in her bill, perched at the entrance to fling them to the side, then slipped back down into the hole and hammered some more.
The male stayed in the vicinity and occasionally made a series of long, nasal calls that sounded like aank. Now and then he flew to the nest hole, peeked in, and chattered to her in apparent excitement, but he never set a foot or wing inside the entrance. When she was not excavating, he sometimes aanked continuously for ten minutes at a time. Apparently he was calling her, because when she arrived and entered the hole to resume work he immediately became silent and then left. He seemed to have an active interest in the work, but not in doing it.
Snow fell for two days in the first week of April, then the air warmed. Maple sap gushed into my buckets, and I boiled it until late at night. In the mornings I got a roaring fire going under the evaporator and soon had plumes of steam rising into the cool air.
Waiting for water to evaporate is not usually exciting, but I was not only harvesting syrup; I was gathering other riches as well. The sapsuckers were back: I heard them drum in the woods. I saw a Canada goose sitting on her nest on the beaver lodge at the precise spot where she and her gander had landed on the day they returned (March 13) after their ten-month absence. She was probably already laying eggs. I marked on my calendar that the young would hatch around May 10.
In the afternoon of April 8, the nuthatches were again repeatedly at the nest hole. Again he only looked in and chattered excitedly. But this time, after she went in, there was no more hammering inside or wood chips thrown out. She stayed inside for ten minutes. I suspected that, after about twenty-eight days of work, the nest site was finished. The amount of effort seemed extraordinary: a robin can build its nest in a couple of days, and some birds build hardly any nest at all. These nuthatches had produced a site for the nest, but after nearly a month of work they still had to build it.
Three days later, on the gorgeous clear morning of April 11, the goose was incubating. Mallards were quacking, and wood frogs chorused in the evening after the thin sheets of ice formed over the pond the night before had melted. The female nuthatch made one trip after another to a high branch in an ash tree, where she plucked bits of moss and then dove down off the tree directly to the nest. She chittered excitedly each time she slipped into the cavity. In two or three seconds she emerged and went back to the ash. The male, as usual, stayed in the background and aanked. But occasionally, when she was not inside, he flew to the nest entrance and looked in. At these moments she perched on a twig nearby and quivered her wings as though mimicking a baby bird begging for food, but I did not see him react to her begging.
But two days later, on April 13, when the weather had been cold and the pond had iced over once more, he did arrive at the nest hole with his bill full of grass and what looked like shredded cedar bark. But unlike her, he did not enter the nest. Instead, he perched at the entrance hole, dropped the material inside, and then perched upside down, and after a while poked his head back into the hole for a peek.
She no longer brought anything to the nest, and she stayed in it while he occasionally passed or dropped small items to her. Sometimes she poked her head out and I heard soft whispering calls or conversations between the two. These were, apparently, preliminaries to mating.
On April 20, at dawn, he flew to the nest hole several times in succession and twittered there, while she stayed inside. Sometimes he left, came back in a few minutes with something in his bill that he passed to her, lingered at the entrance twittering softly, then hopped onto a nearby branch and seemed to wait. Again he went to the entrance, appeared to talk with her, and flew back to the same perch to wait once more. Finally at 6:30 a.m., after he had done this several times, she suddenly shot out of the nest hole and perched on a twig a meter from it, where he joined her and they mated—all within one second. They repeated almost the same pre-mating and mating pattern on subsequent mornings.
There were now long periods when there was no activity at the nest.
By April 21 I had the impression that she was staying in the nest overnight and he was spending the nights outside. I heard him in the pine grove every morning before first light.
On the next morning I arrived in the dark and waited at the base of the tree. I did not see her enter the nest, and since she later came out she surely had spent the night there. He first visited her at dawn, peeking in and soft-chittering with her, then suddenly went on a nest-material-hunting binge, making seven trips between 6:26 and 6:57 a.m. Now, after twenty-eight days of house making and several days of nest making, it was surely time for egg laying. Given a normal clutch of six or seven eggs, one arriving each day, I expected incubation to start in a week.
By May 7 the female was staying inside the nest hole more or less continually, presumably incubating. I had constructed a platform of boards in an adjacent tree where I could perch to watch them from two meters away; they paid me no apparent attention. The male usually came from his overnight quarters in the pine grove at around 6 a.m. to chitter to her at the nest hole, and as always she responded with soft whisper sounds from the nest. Then he left, and sometimes she accompanied him briefly. She did not respond to his long aank calls in the distance. But whenever he came near the nest tree he signaled to her in a softer call, and she instantly responded with soft chittering calls from the nest, then popped up to the nest hole and peeked out, as he flew to her, and they engaged in an almost musical vocal exchange that would have been barely audible to me if I hadn’t been right next to them. Sometimes when he arrived giving his invitation calls she flew out the hole and they met on a branch, where he offered her a morsel of food he had brought and she immediately swallowed it. Since the ever-hungry young would normally get feeding preference, I assumed that the eggs had not yet hatched. She never stayed outside the nest hole more than six minutes, but in that time she often foraged briefly, pecking at what may have been tiny insects on leaves and branches.
During the second week in May he continued to feed her what looked like crane flies and spiders. But apparently this diet was not enough to satisfy her appetite, because on her short periods away from the nest, now always with him, they flew to my feeder and took black sunflower seeds. They carried one seed at a time to a nearby maple tree and wedged it into a crack of the hard bark to hold it while they hammered it open.
When they returned to the nest tree, she often continued to forage in
its vicinity. At these times he appeared anxious to get her to resume incubating. He indicated his impatience by perching on a twig a meter from the nest entrance and vibrating his wings and tail. If she did not immediately fly back to the nest, he flew to it, looked in, and again began to vibrate. At that point, with him giving the signal at the nest site itself, she invariably flew over, slipped inside, and resumed incubating the eggs.
I was away for six days at the end of May. During my absence there were three cold days with incessant rain, and temperatures at night dropped to near freezing. When I came back the birdfeeder was empty and the suet was gone.
I had looked forward to seeing the nuthatches feed their young. But instead, watching the nest on May 31 in my usual dawn session, I saw and heard nothing—absolutely no sign of a nuthatch. Then at 6:30 a.m., when I was ready to leave, I faintly heard the male calling from some distance. I stayed. He came to a nearby pine and called for thirty-six minutes without a single break, behavior I had never observed before. And I saw no sign of her. Finally she arrived, silent, at the nest hole and went in. After some moments I heard hammering from inside for a second or two, then quiet. Within thirty seconds she re-emerged, still silent, and flew away.
Her two-second bout of hammering would not have occurred during egg laying or incubation or in the presence of young. Perhaps it was a displacement activity, something nonfunctional that animals do when they are frustrated and don’t know what else to do. I realized then that the nest had failed.
One Wild Bird at a Time Page 8
